2.0 Chapter Overview

In Chapter 1, we talked about spontaneous breathing as an elegant and effortless process. Comparing spontaneous breathing to mechanical ventilation is like comparing a gentle stream to powerful rapids. During mechanical ventilation, the diaphragm is being bypassed, or in many cases (i.e., sedation, paralysis) knocked out completely. Air is pushed in by generating a high pressure outside the lungs. Mechanical ventilation pushes air into the lungs with a driving force that is generated inside the ventilator and delivered into the lungs through the ventilator circuit and endotracheal tube. We are now dealing with a positive pressure being applied to the lungs instead of the negative pressure that is usually generated with spontaneous breathing via the diaphragm. This driving force (or positive pressure) can be very traumatic to the fragile alveoli in the lungs—imagine wanting to water your garden but instead of a sprinkler, you use a power washer—however, you will begin to learn how to minimize this trauma for the patient while ensuring effective oxygenation.

In this chapter, we will learn why and when mechanical ventilation is used, and the physiology of a mechanically delivered breath. We will explore supplemental oxygen and its impact on the body. Finally, we will revisit PEEP and FiO₂, but this time within the context of mechanical ventilation.

Mechanical ventilation has evolved so much since its infancy, and it is a constantly changing world. In particular, medical researchers have extensively studied the effects of positive pressure ventilation and how traumatic it is to the lungs. Interrupting the physiological process of breathing is never a good thing, and scientific advances are constantly trying to improve medical treatments to mimic the natural breathing process and rhythm. At the end of the day, as close to “natural” as you can achieve is better for the body and safer for the lungs. As such, there is a constant drive to update and improve modes of ventilation and ways to deliver breaths to mimic the natural physiologic process more closely.

As technology improves and ventilators become more advanced, more and more changes and ventilation modes and strategies are continually introduced. This chapter briefly describes causes of respiratory failure in the context of mechanical ventilation requirements, but it is not meant to replace a detailed pathophysiology textbook or resource. Pairing this information with a general understanding of lung mechanics provides a competent understanding of methods to decrease damage to the lungs and how to use ventilator settings to facilitate lung protective strategies. These concepts can be applied to most ventilation modes and strategies. Lung protective strategies will be explored further in later chapters.

Application

It is essential that any respiratory therapy student who is working with ventilators, understand mechanical ventilation and be familiar with all of the ventilator settings in order to learn more about achieving goals for patient care.

“Chapter 3 | Basic Ventilator Modes and Settings” from Basic Principles of Mechanical Ventilation by Melody Bishop, © Sault College is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.